Method and device for sensing humidity with reversible molecular dimerization

Abstract

The present invention relates to the use of reversible dimerization of methylene blue (MB) for sensing humidity. The invention preferably uses titanate nanowires coated with MB. The self-organizational properties of MB on the surface of this nanostructured material studied by spectroscopic means revealed that the light absorption properties of the MB molecules are humidity dependent. Based on the observed humidity dependent metachromasy, we fabricated a humidity sensor using optical fiber technology which is adapted for medical, industrial or environmental applications. The sensor operates with excellent linearity over the relative humidity (RH) levels ranging from 8 to 98%. The response and recovery time can be reduced to 0.5 s while the device exhibits excellent reproducibility with low hysteresis. These performances allow the implementation of the sensor in a breathing monitoring system. Furthermore, the metachromasy was observed for other dyes. This calls for a detailed study of molecular configuration on functional surfaces since it can substantially modify the sensitization efficacy of dyes, e.g. in light conversion.

Description

TECHNICAL FIELD[0001]The present invention relates to the measurement of humidity. The present invention may be used for medical, industrial or environmental applications.BACKGROUND OF THE INVENTION[0002]The physico-chemical process of light conversion is yet under intensive investigation in order to develop more efficient devices for artificial photosynthesis, water splitting and photovoltaic applications.1 The photo-processes of these systems are induced by nanostructured functional materials light sensitized by dye molecules adsorbed on their surface.2 The quantum yield of light conversion drastically depends on the absorption spectrum of the dye. Metachromasy, being the change of the absorption spectrum of dyes without modification of the structural skeleton of the molecule, can be the result of unexpected order / disorder in the assembly of the dye molecules as well as the result of molecular conformation modifications when adsorbed on the functional material surface.3,4 Although...

AI Technical Summary

Benefits of technology

The present invention relates to a new method for sensing humidity using cationic dyes, specifically methylene blue, rhodamine 6G, basic green or auramine ◯. The dyes are adsorbed on titanate nanowires or coated onto optical fibers. The cationic dyes undergo reversible dimerization in response to humidity, resulting in changes in the intensity of light absorbance. The invention provides a high-sensitivity, reversible humidity sensor for a variety of applications, including breathing monitoring systems for detecting hyperventilation. The method is simple and cost-effective to manufacture.

Problems solved by technology

Metachromasy, being the change of the absorption spectrum of dyes without modification of the structural skeleton of the molecule, can be the result of unexpected order / disorder in the assembly of the dye molecules as well as the result of molecular conformation modifications when adsorbed on the functional material surface.3,4 Although metachromasy can be detrimental for device performance, possible factors influencing the absorption spectrum of the dye are largely unexplored.

This matter has not yet received appropriate attention in the case of nanowires as well as for conventional isotropic nanoparticles.

So far, efficient devices have not been realized yet.

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